The invention relates to pressure-sensitive adhesives having both a high moisture vapor transmission rate (MVTR) and good skin adhesion.
Adhesive laminates used in medical products such as medical tapes, wound care dressings, and consumer bandages need a high MVTR to allow the escape of moisture generated by the skin or by wound exudate. A high MVTR of the laminate prevents moisture from being trapped under the dressing, which could otherwise cause maceration of the skin. High MVTR films are commercially available, but once coated with a pressure-sensitive adhesive (PSA) they typically exhibit a dramatic drop in MVTR, due to the low MVTR of the adhesive layer. Discontinuous coating of the adhesive can be used to achieve a high MVTR of the laminate, however, the laminate no longer serves as a bacterial barrier, necessary for wound care dressings, and discontinuous coating processes are expensive.
To meet Government regulations and customer demands, it is often necessary to gamma irradiate or otherwise sterilize MVTR films and adhesive constructions. Unfortunately, gamma irradiation can diminish the adhesiveness of an MVTR adhesive product. The problem is exacerbated if the product is inadvertently (or purposely) exposed to a double dose of radiation, i.e., 50 kGy instead of the standard 25 kGy dose.
What is needed is an adhesive that has a high MVTR, even when coated as a continuous film, without sacrificing good skin adhesion, so that the edges of the laminate do not lift off the skin during the wear time of the dressing, typically 24 hours. The adhesive should be able to withstand gamma irradiation sterilization without a substantial loss of adhesive strength. The cohesive strength of the adhesive should be sufficiently high to prevent any adhesive residue from being left on the skin upon removal of the adhesive laminate. The adhesive also should be skin-friendly and cause no irritation or cytotoxicity.
According to the present invention, PSAs and adhesive constructions characterized by high MVTR and good skin adhesion are provided. The PSAs comprise acrylic copolymers formed from a plurality of monomers, and have a composition, glass transition temperature (Tg) and weight-average molecular weight (Mw) that facilitate high MVTR values and good skin adhesion. Adhesive constructions, i.e., medical tapes, wound care dressings, bandages, and similar products are also provided, and comprise a high MVTR PSA coated on or otherwise applied to a water vapor-permeable backing.
A key advantage of the present invention is the balancing of MVTR and skin adhesion. A desirably high MVTR (i.e., greater than or equal to about 1,900 g/m2/day, more preferably greater than or equal to 2,000 g/m2/day) is realized by selecting the monomeric composition and coat weight in the manner described herein. At the same time, excellent skin adhesion is realized through careful control of molecular weight, gel content, and glass transition temperature.